A variety of monomers, oligomers and polymers containing ethynyl (acetylenic) and substituted ethynyl (i.e., phenylethynyl) groups have been reported. The ethynyl groups in the polymer are either pendent to the chain, in the chain or at the chain ends. Many of these materials have been used to prepare coatings, moldings, adhesives and composites [P. M. Hergenrother, xe2x80x9cAcetylene Terminated Prepolymersxe2x80x9d in Encyclopedia of Polymer Science and Engineering, John Wiley and Sons, New York, Vol. 1, 61 (1985)]. Good processability by either solution casting and/or compression molding have been observed for the ethynyl and substituted ethynyl containing materials. In general, thermally cured ethynyl and substituted ethynyl containing materials exhibit a favorable combination of physical and mechanical properties. Some ethynyl endcapped materials such as the Thermid(copyright) resins are commercially available (National Starch and Chemical Co., Bridgewater, N.J. 08807). Other systems such as acetylene terminated sulfone have undergone extensive evaluation as matrix resins [M. G. Maximovich, S. C. Lockerby, F. E. Arnold and G. A. Loughran, Sci. Adv. Matls. Proc. Eng. Ser., 23, 490 (1978) and G. A. Loughran, A. Wereta and F. E. Arnold, U.S. Pat. No. 4,131,625, December 1978 to U.S. Air Force].
Phenylethynyl containing amines have been used to terminate imide oligomers [F. W. Harris, A. Pamidimuhkala, R. Gupta, S. Das, T. Wu, G . Mock, Poly. Prep., 24 (2), 325, 1983; F. W. Harris, A. Pamidimuhkala, R. Gupta, S. Das, T. Wu, G. Mock, Macromol. Sci.-Chem., A21 (8and9), 1117 (1984); C. W. Paul, R. A. Shultz, and S. P. Fenelli, xe2x80x9cHigh Temperature Curing Endcaps for Polyimide Oligomersxe2x80x9d in Advances in Polyimide Science and Technology, (Ed. C. Feger, M. M. Khoyasteh, and M. S. Htoo), Technomic Publishing Co., Inc., Lancaster, Pa., 1993, p. 220; R. G. Bryant, B. J. Jensen, P. M. Hergenrother, Poly. Prepr., 34(1), 566, 1993]. Imide oligomers terminated with ethynyl phthalic anhydride [P. M. Hergenrother, Poly. Prepr., 21(1), 81, 1980], substituted ethynyl phthalic anhydride [S. Hino, S. Sato, K. Kora, and O. Suzuki, Jpn. Kokai Tokyo Koho Japanese Patent #63,196,564. Aug. 15, 1988; Chem. Abstr., 115573w, 110, (1989)] and phenylethynyl containing phthalic anhydrides have been reported. Imide oligomers containing pendent substituted ethynyl groups [F. W. Harris, S. M. Padaki, and S. Varaprath, Poly. Prepr., 21(1), 3, 1980 (abstract only); B. J. Jensen, P. M. Hergenrother and G. Nwokogu, Polymer, 34(3), 630, 1993; B. J. Jensen and P. M. Hergenrother, U.S. Pat. No. 5,344,982 (Sep. 6, 1994)] have been reported. See also J. E. McGrath and G. W. Meyer, U.S. Pat. No. 4,493,002 (Feb. 20, 1996), J. G. Smith, Jr. Adhesion Society Proceedings, Vol. 19, 29-32 (1996) and J. W. Connell, J. G. Smith, Jr. And P. M. Hergenrother, Society for the Advancement of Materials and Process Engineering Proceedings, Vol. 41, 1102-1112 (1996).
High temperature resins are used in a variety of aerospace and non-aerospace applications. Generally these materials require high pressures ( greater than 200 psi) to form adhesive bonds, well consolidated moldings or fiber reinforced composite laminates. However, there exists a need for novel high temperature resins that can be processed at low pressures and without an autoclave (i.e., under vacuum bag conditionsxe2x80x94xcx9c15 psi) while maintaining excellent mechanical properties.
It is a primary object of the present invention to provide novel phenylethynyl containing reactive additives (PERAs) which can be used with any phenylethynyl containing polymer, co-polymer, oligomers or co-oligomers to decrease melt flow and consequently processing pressures required to fabricate molded parts, adhesive bonds, and fiber reinforced composite parts.
According to the present invention the forgoing and additional objects are obtained by synthesizing amide acid and imide phenylethynyl reactive additives, subsequently adding them to phenylethynyl containing polymers, co-polymers, oligomers and co-oligomers in solution or by mixing dry imide powder of the reactive additive with phenylethynyl containing oligomer powder. These species can be combined in several different ways: as solutions of amide acid of the phenylethynyl containing reactive additive (PERA) to a solution of the phenylethynyl containing polymer, co-polymer, oligomer, co-oligomer; as solutions of the imide of the PERA to solutions of the phenylethynyl containing polymer, co-polymer, oligomer, co-oligomer and by dry mixing of the imide powder of the PERA to the dry powder of the phenylethynyl containing polymer, co-polymer, oligomer, co-oligomer. The effect of these reactive additives on the processability and properties on the resin systems depends upon the form of the PERA (i.e., imide vs. amide acid) used.
The PERA reduce the melt viscosity of the phenylethynyl containing polymer, co-polymer, oligomer, and co-oligomer to which they are added and thereby reduce the processing pressures required to form the adhesive bonds, consolidated filled or unfilled moldings or to fabricate fiber reinforced composite laminates. Upon thermal cure the PERAs react with themselves as well as with the phenylethynyl containing host resin and thereby become chemically incorporated into the resin system. The effect on mechanical properties, relative to those of the host resin, are dependent on the amount of PERA used, but typically result in higher Tgs, higher mechanical properties such as modulus and compressive properties as well as higher retention of these mechanical properties at elevated temperatures without significantly reducing toughness or damage tolerance (as determined by compression after impact strengths of quasi-isotropic laminates).